Various kinds of blood treatment apparatuses are known. The known blood treatment apparatuses include, for example, the apparatuses for hemodialysis, hemofiltration and hemodiafiltration. During the blood treatment, the patient's blood flows in an extracorporeal blood circuit through a blood treatment unit. In the case of the apparatuses for hemodialysis, hemofiltration and hemodiafiltration, the blood treatment unit is a dialyzer or filter, which is divided by a semi-permeable membrane into a blood chamber and a dialyzing fluid chamber. During the blood treatment, the blood flows through the blood chamber, while the dialyzing fluid flows through the dialyzing fluid chamber. An effective blood treatment requires that blood and dialyzing fluid flow in opposite directions along the membrane of the dialyzer or filter. In the case of an equi-directional flow, the blood treatment is less effective. In practice, therefore, the dialyzer or filter is operated not with an equi-directional flow, but with a counter-flow.
The dialyzer or filter is an interchangeable unit, which is connected to the fluid system of the blood treatment apparatus. The fluid system of the known blood treatment apparatuses comprises a line system with a first and a second line segment for the connection of the dialyzer. For the connection of the dialyzer to the fluid system, the first line segment is connected to the inlet of the dialyzing fluid chamber and the second line segment is connected to the outlet of the dialyzing fluid chamber of the dialyzer. The connection of the dialyzer takes place with known connection pieces, which include the known Hansen couplings.
The manufacturers of dialyzers and blood treatment apparatuses provide a color coding of the inlet and outlet of the dialyzer and of the Hansen couplings to be connected to the inlet and outlet, in order to make it easier for the user to make the connection according to the counter-flow principle. This color coding, however, is not uniform with all manufacturers. There is therefore the risk of the connections being confused. This will be referred to below as an incorrect connection.
If the dialyzer is not operated with a counter-flow, but with an equi-directional flow, the effectiveness of the treatment for the patient may be inadequate. This is particularly problematic when an incorrect connection of the dialyzer remains unnoticed. There is then the risk of the patient being treated with inadequate efficiency over a long period.
The problem underlying the present invention is to provide a device and a method for detecting the direction of the fluid flow through a dialyzer, in order to be able to check whether the dialyzer is being operated with an equi-directional flow or with a counter-flow. Moreover, the problem of the present invention is to provide an extracorporeal blood treatment apparatus with which the reliability in dialysis is increased.
The device according to the present invention and the method according to the present invention permit the monitoring of the connection of a dialyzer to the fluid system of an extracorporeal blood treatment apparatus. The detection of the direction of the fluid flow through the dialyzer of the extracorporeal blood treatment apparatus is based on the change in a physical and/or chemical property of a fluid flowing into the one chamber of the dialyzer and the measurement of the change in the physical and/or chemical property of the fluid flowing out of the one chamber of the dialyzer. The change in the physical and/or chemical property of the fluid downstream of the one chamber of the dialyzer traced back to the change in the physical and/or chemical property upstream of the one chamber of the dialyzer is measured before and after the reversal of the flow direction of the fluid through the one chamber of the dialyzer. A second fluid flows through the other chamber of the dialyzer, the flow direction whereof remains unchanged.
The flow reversal can take place in the whole fluid system or only in parts of the fluid system. For the flow reversal in the whole fluid system, the delivery direction of the delivery pump in the fluid system can be reversed. For the fluid reversal only in parts of the fluid system, a valve arrangement constituted in the manner of points can be used.
If the change in the physical and/or chemical property of the first fluid upstream of the one chamber of the dialyzer is known, the change in the physical and/or chemical property of the first fluid does not need to be measured. In the case where the physical and/or chemical property of the first fluid upstream of the one chamber of the dialyzer is however not known, the physical and/or chemical property of the first fluid is measured both upstream and downstream of the dialyzer.
The change in the physical and/or chemical property can take place through an increase and/or reduction of the physical and/or chemical property, whereby the change in the physical and/or chemical property can take place before and after the reversal of the flow direction by the same amount or different amounts. The physical and/or chemical property of the fluid is preferably changed by the same amount, which is preferably known. In this case, the change in the physical and/or chemical property only needs to be measured downstream of the one chamber of the dialyzer.
The first fluid flowing through the one chamber of the dialyzer can be dialyzing fluid, while the second fluid flowing through the second chamber of the dialyzer can be blood. In this case, the flow direction of the dialyzing fluid is reversed in the one chamber of the dialyzer. In principle, however, it is also possible to reverse the flow direction of the blood in the other chamber of the dialyzer.
If dialyzing fluid is flowing through the one chamber of the dialyzer and blood is flowing through the other chamber of the dialyzer, the detection of the flow direction through the dialyzer can take place during the blood treatment. It is however also possible to check the flow direction through the dialyzer before the blood treatment, if other fluids are flowing through the chambers of the dialyzer. Rinsing fluid can, for example, flow through one of the two chambers of the dialyzer.
For the detection of the flow direction through the dialyzer, it is basically irrelevant which physical and/or chemical property is changed. The concentration of a substance, for example the Na concentration, in one of the two fluids is preferably changed. It is however also possible to change the temperature of the fluid.
The change in the quantity of substance can easily take place in the dialysate preparation of the extracorporeal blood treatment apparatus. The temperature of the dialyzing fluid can also be changed in the dialysate preparation. The measurement of the concentration of a substance or the temperature of the fluid can take place with the known sensors, which are in any case generally present in the known blood treatment apparatuses. The method according to the present invention and the device according to the present invention can therefore easily be implemented in the known blood treatment apparatuses.
A preferred embodiment of the present invention makes provision to calculate the integral over the physical and/or chemical property of the fluid flowing into the first chamber of the dialyzer and the integral of the fluid flowing out of the first chamber of the dialyzer before and after the reversal of the flow direction, the operation of the dialyzer before the reversal of the flow direction with an equi-directional flow or with a counter-flow being determined on the basis of a comparison of the difference between the two integral values after the reversal of the flow direction with the difference between the two integral values before the reversal of the flow direction. The quotient of the difference between the two integral values after the reversal of the flow direction and the difference between the two integral values before the reversal of the flow direction is preferably calculated, it being concluded that there is an operation of the dialyzer before the reversal of the flow direction with an equi-directional flow if the quotient is greater than 1 or it being concluded that there is an operation of the dialyzer before the reversal of the flow direction with a counter-flow if the quotient is less than 1. In order to calculate the integral over the physical and/or chemical property, the area is calculated which is enclosed by the graph, which describes the physical and/or chemical property as a function of time, and the base line, which represents the constant quantity of the physical and/or chemical property. The points of intersection of this graph with the base line running parallel to the time axis define the integration limits. Only the pulse which is plotted on the base line is therefore integrated.
If a correct operation of the dialyzer is the operation with a counter-flow, an alarm, preferably an optical and/or acoustic and/or tactile alarm, is preferably emitted if it is established that, before the reversal of the flow direction, it can be concluded that there is an operation of the dialyzer with an equi-directional flow. In the case of an incorrect operation, a control signal for intervention into the machine control is preferably generated. The intervention into the machine control can consist in the fact that the performance of the blood treatment is prevented. This ensures that the blood treatment is only possible with a correct connection of the dialyzer. It is however also possible, as an intervention into the machine control, to reverse the flow direction so that the dialyzer is then operated correctly.